LI

Question 1

ileocaecal valve

Answer 1

muscular sphincter 
separates distal ileum from ceacum 
tonically active and constricted 
only relax to allow chime into LI 
prevent bacteria entering ileum

Question 2

caecum

Answer 2

blind pouch

distal to ileocaecal calve

Question 3

appendix

Answer 3

extension from caecum
limited role
safe refuge for gut bacteria after diaorrea

Question 4

colon

Answer 4

ascending - start at ileocaecal valve -> hepatic flexure on the R side of the body
transverse - start at hepatic flexure and run across abdomen -> splecic flexure
descending - start at splenic flexure and runs to 1st bend of igmoid
sigmoid - S shaped runs to rectum

Question 5

rectum

Answer 5

dilated portion
act as a storage site
has transverse rectal folds in submucosa - shelves for faeces
no taeniae coli in muscularis externa

Question 6

anal canal

Answer 6

control movement of things out of GI
2 anal sphincters
sm under central control - internal sphincter
external muscle is striated and under vol control by pudendal nerves

Question 7

appendix epiploicae

Answer 7

fatty tags from serosa
no physiological function
perhaps protective against intraabdominal infections

Question 8

longitudinal muscle

Answer 8

3 bands longitudinal muscle
equally spread around the circumference
thicker than typical longitudinal layers
shorter than colon - colon forms lpouches called hastra

Question 9

circular muscle

Answer 9

segmentally thickened

bundles of muscle from taeniae coli penetrate to keep it together

Question 10

nodules of lymphoid tissue

Answer 10

usually solitary nodules

Question 11

components of the LI

Answer 11

colon
cecum 
appendix 
rectum 
anal canal

Question 12

size of the colon

Answer 12

1.5m long, 6cm diameter

Question 13

Edit Delete

attachment of transverse colon

Answer 13

hangs off the stomach

attached by the greater omentum

Question 14

blood supply of the colon

Answer 14

proximal transverse colon upplied with blood by middle colic artery (branch of superior mesenteric artery)
distal 1/3 - inferior mesenteric artery
reflects the embryonic division between mid and hind gut

Question 15

consequence of colon have 2 blood supplies

Answer 15

area between is sensitive to ischemia in haemorrhage

Question 16

gut wall

Answer 16

peritoneum has fatty tags
muscle coat has 3 thick longitudinal bands - taeniae coli
gut wall is pouched - haustra
nodules of lymphoid tissue common in walls of distal small intestine - peyer’s patches, and LI - solitary nodules for communication between gut immune system and microbiome

Question 17

function of tenia coli

Answer 17

large intestine motility

Question 18

Haustra

Answer 18

taenia coli shorter than in SI
cause pouched ovoid segments - haustra
not always in same place - muscle tone

Question 19

general plan of the gut tube

Answer 19

serosa
longitudinal muscle 
circular muscle 
muscularis 
lamina propria 
epithelium

Question 20

comparision of the structure of the LI and SI

Answer 20

in both:
enterocytes and goblet cells
abundant crypts
stem cells in crypts

Question 21

LI mucosal organisation

Answer 21

appears smooth - no villi 
enterocytes (luminal side) have short irregular microvilli - reabsorption of salts and macronutrients 
crypts have goblet cells 
no Paneth cells 
fewer enteroendocrine cells than SI 
glycocalyx - no digestive enzymes

Question 22

goblet cells in LI

Answer 22

more than in SI
more distal
mucus fascilitate passage of more solid contents, covers bacteria and particulate matter
stimulated by ACh - PNS and enteric NS - plexuses in wall of gut

Question 23

why no Paneth cells in the LI

Answer 23

would kill flora
commensal is important
less bacteria than in SI - food already been digested

Question 24

muscle layers of LI

Answer 24

muscularis externa - inner circular and outer longitudinal layer
circular are segmentally thickened
longitudinal concentrated in 3 bands - taenia coli
bundles from here penetrate the circular
between taenia longitudinal is thin
longitudinal shorter than circular = haustra = contract individually

Question 25

components if the large intestine

Answer 25

``` colon caecum appendix eecctum anal canal ```

Question 26

main func of the colon

Answer 26

reabsorption of water and electrolytes elimination of waste microenvironment for gut bacteria

Question 27

structure of the LI

Answer 27

150cm long 6cm wide receives blood from middle colic artery - perfuses ascending and 1st 2/3 of transverse and from inferior mesenteric artery - perfuse last 1/3 transverse, descending colon, sigmoid colon and rectum

Question 28

innervation of the LI

Answer 28

PNS - vagus innervate ascending and most of transverse distal colon innervated by pelvic nerves sympathetic innervation arises from lower thoracic and upper lumber spinal cord

Question 29

reabsorption

Answer 29

ions and water in proximal colon mainly contents become dehydrated na and cl are exchange mechanisms - water follows K moves passively into lumen through tight junctions capacity to absorb 4.5L but only absorbs 1.5l - SI ddoes more

Question 30

describe the cells of the colon

Answer 30

many goblet and enterocytes colonic crypts - stem cells at bottom smootgh mucosa - no villi = small sa - less absorption enterocytes have small irregular microvilli enterocyte structure reflects resorbative function

Question 31

goblet cells

Answer 31

line the crypts secrete mucus to help passage - abundance increase along colon mucous also cover bacteria and particulate matter stimulated by ACh

Question 32

Paneth cells

Answer 32

absent in LI because of commensal bacteria

Question 33

enteroendocrine cells

Answer 33

less than in SI - absorption is simpler

Question 34

glycocalyx

Answer 34

present | doesn't contain the digestive prush border enzymes

Question 35

motility - basic contractions

Answer 35

kneading process - minimal propulsion - allow chime to stay in colon for a long time = more absorption proximal colon has antipropulsive contractions to keep food for longer transverses and descending - localised segmental contractions of circular muscle - haustral contractions - shuffle contents forwards and backwards short propulsive movements every 30mins - more after eat - clear for next food

Question 36

motility - mass movement

Answer 36

1-3 times a day propel contents 3/4 of length in a few seconds high fibre food, coffee, smoke promotes mass movement

Question 37

faeces

Answer 37

``` indigestible waste 2/3 water cellulose bacteria = smell cell debris- lose because cant digest them in the SI bile pigments/salts ```

Question 38

defaecation

Answer 38

suddenly after mass movement - feel the need pressure receptors send ssignals - myenteric plexuys to initiate peristaltic waves - inhibit internal sphincter weak signal is helped by autonomic relflex from the brain internal anal sphincter is relaxed in defecation reflex - via sacral spinal cord - reflex and voluntary detention of wall detected by pressure receptors signals to myenteric plexus to initiate peristaltic waves in descending, sigmoid colon and rectum

Question 39

what determines when it is appropriate to defecate

Answer 39

last bit rectum can detect between solid, liquid and gas | difficult to distinguish between gas and oil = spotting of underwear - especially with Orlistat

Question 40

control of the colon

Answer 40

PNS - ascending and 2/3 transverse innervated by vagus 9acid from stomach and enzyme part of pancreatic juice, distal - pelvic nerve sympathetic - lower thoracic and upper lumbar spinal chord external anal sphincter - somatic fibres - pudendal nerves afferent sensory detect pressure

Question 41

enteric control of the LI

Answer 41

myenteric plexus ganglia below taenia coli prescence of food stimulate mass movement involved in coeliac loss of enteric = Hirschsprung's disease

Question 42

hormonal control of LI

Answer 42

aldosterone - Na and H2O reabsorption | by synth channel and Na/K pump

Question 43

where is bile salt reabsorbed

Answer 43

terminal ileum

Question 44

physiological role of the LI microbiome

Answer 44

form a symbiotic relationship Synthesise and excrete Vitamin K - for coag prevent pathogens - compete antagonise bacteria that kill/inhibit non-indigenous species stimulate production of cross reactive Ab stimulate development of tissues fibre break down produce short chain FA - receptor in gut, panc, vagus and adipose - signal molecules - regulate gut hormone release/energy source/influence food intake/insulin sensitivity links with drug metabolism, insulin resistance, bile acid metabolism, lipid metabolism and obesity produce short FA - regulate gut hormone release

Question 45

location of bacteria

Answer 45

few in stomach/ proximal si - harsh environment

Question 46

prevalent species

Answer 46

bacteriodetes gram -ve anaerobic non-spore forming

Question 47

pathophysiology

Answer 47

gut bacteria prime immune system inappropriate pop of commensal = predispose infection potential value in faecal transplant to reinstate bacteria

Question 48

large intestinal flora

Answer 48

Trillions of bacteria size of an organ have to look phylogenetically

Question 49

flora and colitis or colon cancer

Answer 49

changes composition

Question 50

bifidobacteria

Answer 50

``` gram +ve non-spore forming lactic acid bacteria friendly prevent colonisation by potential pathogens ```

Question 51

links between gut bacteria and other systems

Answer 51

``` drug met insulin resistance bile acid met - hydroxyl gp removed so it easier to be absorbed lipid met obesity cancer ```